Patent GB-980975-A (GB)
Title: Improvements in or relating to methods of forming metallized surfaces on ceramic bodies
IPC: C04B41/88
Filed: 1962-09-17
Abstract: A metallized surface is imparted to a ceramic body (e.g. one of 98% by wt. of alumina, beryllia or a mixture of alumina and beryllia) by coating at least a portion of the surface of the body with a mixture of powdered metal (of which the major part may be molybdenum and/or tungsten) and powdered glass, the powdered glass constituting not more than 30% by weight of said mixture, and having a coefficient of thermal expansion comparable with that of the body, the lowest temperature at which appreciable sintering of the powdered metal occurs lying between the temperature at which the glass becomes a mobile liquid and the temperature at which the body becomes a mobile liquid, and then subjecting the coated body to two consecutive periods of firing during the first of which the firing temperature has a value between the temperature at which the glass becomes a mobile liquid and the lowest temperature at which appreciable sintering of the powdered metal occurs, and during the second of which the firing temperature has a value between said lowest temperature of sintering and the temperature at which the body becomes a mobile liquid.  The glass used may have a composition by weight of SiO2 10%; Al2O3 37.1%; CaO 45.9%; MgO 5.0%; SrO 2%; or may be a lime-alumina-silica or magnesia-alumina-silica glass exhibiting a gehlenite structure when devitrified. The first-mentioned glass becomes a mobile liquid at a temperature of 1400 DEG  C. and has a coefficient of thermal expansion of 8.97 x 10-6 per  DEG C.  The lowest temperature of sintering of molybdenum is 1450 DEG  C., and the temperature at which a body of 99.5% alumina becomes a mobile liquid is about 2000 DEG  C.  The firing for this combination would be ten minutes at 1430 DEG  C. and five minutes at 1600 DEG  C. Firing is in an atmosphere of pure hydrogen.ALSO:A metallized surface is imparted to a ceramic body (e.g. one of 98% by weight of alumina, beryllia or a mixture of alumina and beryllia) by coating at least a portion of the surface of the body with a mixture of powdered metal (of which the major part may be molybdenum and/or tungsten and the minor part manganese, iron, nickel or palladium) and powdered glass, the powdered glass constituting not more than 30% by weight of said mixture, and having a coefficient of thermal expansion comparable with that of the body, the lowest temperature at which appreciable sintering of the powdered metal occurs lying between the temperature at which the glass becomes a mobile liquid and the temperature at which the body becomes a mobile liquid, and then subjecting the coated body to two consecutive periods of firing during the first of which the firing temperature has a value between the temperature at which the glass becomes a mobile liquid and the lowest temperature at which appreciable sintering of the powdered metal occurs, and during the second of which the firing temperature has a value between said lowest temperature of sintering and the temperature at which the body becomes a mobile liquid.  A mixture comprising 90% molybdenum and 10% of a glass exhibiting a gehlenite structure when devitrified may be used (e.g. a glass SiO2 10% ; Al2O3 37.1% ; CaO 45.9% ; HgO 5.0% ; SrO 2.0%). The glass mentioned becomes a mobile liquid at 1400  DEG C. and has a coefficient of expansion of 8.47 x 10-6 per  DEG C.  The lowest temperature of sintering of the molybdenum is 1450  DEG C. and the temperature at which a body of 99.5% alumina becomes a mobile liquid is about 2000  DEG C.  The firing for this combination would be ten minutes at 1430  DEG C. and five minutes at 1600  DEG C.  The firing is done in an atmosphere of hydrogen.